Electrophoresis is a process that can be used to analyze substances. An example of an electrophoretic analysis is DNA sequencing, which is a type of analysis undertaken to analyze the genetic sequence of a sample of DNA. In one type of electrophoretic DNA sequencing, a polyacrylamide gel is held between two plates of a so-called cassette, and the DNA sample to be analyzed is deposited on the gel. If desired, the DNA sample can be tagged with a radioisotope for manual electrophoresis sequencing or the DNA sample can be tagged with a fluorescent substance for automatic DNA sequencing. Then, the cassette is placed in or conveyed through an electrophoresis apparatus for exposing the gel to an electric field. Under the influence of the electric field, the various constituents in the DNA migrate through the gel at various rates depending on their sizes, thereby separating from each other and facilitating analysis of the sample.
In manual electrophoresis, the sample is removed from the electrophoresis apparatus and analyzed by, e.g., x-ray photoimagery of the radioisotope-tagged sample. On the other hand, in automatic electrophoresis the cassette is illuminated with light having a predetermined wavelength to cause the fluorescent tag of the DNA sample to emit fluorescence, which is then detected by a sensor in the electrophoresis apparatus and correlated to a genetic composition. Relatively expensive glass cassettes have heretofore been used in automatic electrophoresis that use principles of fluorescence, because such cassettes, when made of glass instead of plastic, advantageously minimize reflection and/or interference with the relatively weak fluorescence that is typically emitted by fluorescently-tagged DNA samples.
Both manual and automatic electrophoresis can be undertaken by orienting the cassette upright, or vertically, in the electrophoresis apparatus. In vertical electrophoresis, a portion of one of the cassette plates is cutout near the top of the plate, and an upper buffer tank is fastened to the cassette next to the cutout and filled with a buffer solution, such that the solution communicates with the gel in the gel chamber. The lower end of the cassette is then placed in a lower buffer solution and the electric field applied to the gel by means of the upper (cathodic) solution and lower (anodic) solution. To ensure that no buffer solution leaks from between the upper buffer tank and the cassette plate, the buffer tank is formed with a groove, and a resilient gasket is positioned in the groove to establish a seal between the plate and the tank.
As recognized by the present invention, present glass cassettes are both expensive and fragile. Consequently, they are easily broken during shipment from the cassette manufacturer to customer laboratories. The present invention additionally recognizes that the requirement to form the upper buffer tank with a groove for the sealing gasket further increases the cost of the cassette. As recognized herein, however, it is possible to provide an inexpensive yet effective cassette for vertical electrophoresis that can be used in existing electrophoresis apparatus and that nevertheless can be configured for minimizing interference with fluorescence emitted from a DNA sample.
Accordingly, it is an object of the present invention to provide an inexpensive gel cassette for electrophoresis that can be used in existing manual or automatic electrophoresis apparatus. Another object of the present invention is to provide a gel cassette for electrophoresis that does not require a gasket groove to be formed in an upper buffer tank. Still another object of the present invention is to provide a gel cassette for electrophoresis that is made of plastic and that is configured for minimizing interference with fluorescent light from a DNA sample tag. Yet another object of the present invention is to provide a gel cassette for electrophoresis that is easy to use and cost effective to manufacture.